This application claims the benefit of Korean Patent Application No. 2002-25400, filed on May 8, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a high-speed, sensitive semiconductor probe with a resistive tip and a method of fabricating the same, and to an information recording apparatus, an information reproducing apparatus, and an information measuring apparatus having the semiconductor probe.
2. Description of the Related Art
As the demand for small-sized products such as portable communication terminals and electronic notes increases, highly-integrated micro nonvolatile recording media are increasingly required. It is not easy to reduce the size of existing hard disks and to highly integrate flash memories. Thus, information storage media and method using a scanning probe have been studied as a possible alternative.
The scanning probe is used in various types of scanning probe microscopes (SPMs). For example, the scanning probe is used in a scanning tunneling microscope (STM), an atomic force microscope (AFM), a magnetic force microscope (MFM), a scanning near-field optical microscope (SNOM), an electrostatic force microscope (EFM), and the like. The STM detects a current flowing through a probe based on a difference between voltages applied to the probe and a sample to reproduce information. The AFM uses an atomic force between a probe and a sample. The MFM uses a magnetic force between a magnetic field near the surface of a sample and a magnetized probe. The SNOM improves a resolution less than the wavelength of visible light. The EFM uses an electrostatic force between a sample and a probe.
In order to record and reproduce information at a high speed and density using such a SPM, a surface charge in a small area having a diameter of several tens of nanometers should be detected. Also, a cantilever should be made into an array form to increase a recording and reproduction speed.
FIG. 1A is a perspective view of a metal-on-semiconductor field effect transistor (MOSFET) probe of a scanning probe microscope, the MOSFET probe having a MOSFET channel structure, disclosed in Korea Patent Publication No. 2001-45981, and FIG. 1B is an enlarged view of portion A of FIG. 1A.
Referring to FIG. 1A, a MOSFET probe 22, which is formed by etching a semiconductor substrate 20, has a bar-shaped protrusion that protrudes from the semiconductor substrate 20. Electrode pads 20a and 20b face each other on a portion of the semiconductor substrate 20 contacting one end of the MOSFET probe 22.
Referring to FIG. 1B, a source area 11 and a drain area 13 are formed on the slope of a V-shaped tip 10 of the MOSFET probe 22, and a channel area 12 is formed therebetween.
The V-shaped tip of the MOSFET probe 10 having the above-described structure is positioned on the end portion of a cantilever. Thus, it is not easy to make probes having a radius of several tens of nanometers into an array form. In the prior art, in order to manufacture such a probe, a tip having a radius of several tens of nanometers should be manufactured using the various processes including an oxidization process and so forth so that the probe is perpendicular to a cantilever. However, since the precision of a photolithographic process decreases considerably when a tip is formed to a height of several tens of nanometers, it is difficult to form a source area and a drain area so as to make a short channel.
FIGS. 2A and 2B are schematic cross-sectional views for explaining a method of reproducing information using a MOSFET tip in which source and drain areas 11 and 13 are formed. Referring to FIG. 2A, a MOSFET tip 10, which is V-shaped, is doped with p-type impurities. Next, the MOSFET tip 10 is doped with n-type impurities to form source and drain areas 11 and 13 on the slope thereof. The MOSFET tip 10 detects a current flowing through a channel 12 based on the polarity of a surface charge 17 while it moves over the surface of a recording medium 15, in order to detect the polarity and density of the surface charge 17.
FIG. 2B is an enlarged cross-sectional view of the peak of the MOSFET tip 10 for explaining a process of expanding a depletion area 14. Referring to FIG. 2B, when the MOSFET tip 10 is positioned over a positive surface charge 17 in the recording medium 15, holes of the channel 12 doped with p-type impurities move toward the source and drain areas 11 and 13 little by little due to electric fields induced by the positive surface charge 17.
The depletion area 14, from which the holes are depleted due to the movement of the holes, expands. When an electric field greater than an electric field maximizing the size of the depletion area 14 is applied to the peak of the MOSFET tip 10, a channel containing minority carriers is formed at the peak of the MOSFET tip 10. If a greater electric field is applied to the peak of the MOSFET tip 10, a channel containing electrons is connected to the source and drain areas 11 and 13. Then, a current flows through the channel due to a voltage applied between the source and drain areas 11 and 13.
In other words, the MOSFET tip 10 operates as a transistor only if an electric field induced by a surface charge has a value higher than a threshold electric field value that is suitable for expanding a channel containing minority carriers up to source and drain areas. Thus, since a surface charge inducing an electric field that is less than the threshold electric field value cannot be detected, the MOSFET tip 10 operates within a limited range and the sensitivity of the MOSFET probe 10 degrades.